Understanding of C ＃ delegate

1. What is a delegate

Delegation is to delegate a method to achieve specific functions , Be similar to : Party A entrusts Party B to realize the demand ; The lessor entrusts an intermediary to rent the house for him .

A delegate is a reference type , In terms of data structure ： Delegates are like classes , Are user-defined types .

2： The implementation of delegation

Delegation is the abstraction and encapsulation of methods . A delegate object essentially represents a reference to a method （ Memory address ） What he stores is the address of a series of methods with the same signature and return type

It can be understood as a package of functions , It makes the c# Functions in can be passed as parameters

Follow the three-step principle when using ： Define the entrusted 、 Instantiation delegation , The delegate

When invoking a delegate , The methods contained in the delegate will be executed

There are three ways to delegate ： Naming method delegate 、 The multicast delegate 、 Anonymous delegate

  Nomenclature delegation

1: Define the entrusted 
 Modifier  delegate  return type   Name of Commission  { parameter list }

public delegate void FirstDelegate ();

  Instantiation delegate of static method  

2： Instantiation delegation 

 Name of Commission   Delegate object name =new  Name of Commission { Method name }

FirstDelegate firstDelegate=new FirstDelegate(Test.First);
 The method of a delegate can be the name of a static method , It can also be the name of the instantiation method 

 Method ：

public class Test
{

     public static void First()
     {
         Console.WriteLine(" It is the first time to implement the delegation of static method classes ");
     }
}

3: call 

firstDelegate();

Delegate of instantiation method

2： Instantiation delegation 

 Name of Commission   Delegate object name =new  Name of Commission { Method name }

FirstDelegate firstDelegate=new FirstDelegate(new Test().First);
 The method of a delegate can be the name of a static method , It can also be the name of the instantiation method 

 Method ：

public class Test
{

     public  void First()
     {
         Console.WriteLine(" It is the first time to implement the delegation of instantiation method class ");
     }
}

3: call 

firstDelegate();

The multicast delegate  

  Multicast delegation is to register multiple methods in a delegation , When registering methods, you can add or revoke methods by adding or subtracting signs in delegates .

for example I want to buy some rice And I want to have milk tea I also want to eat cake , I can't entrust one person , I need to entrust three people to help me finish , For example, meituan

1： Define the entrusted 

public class problem
{
     public delegate void BuyDelegate();


     static void mian()
     {
         BuyDelegate buyDelegate=new BuyDelegate(Buy.BuyFood);
         buyDelegate+=Buy.BuyCake;
         buyDelegate+=Buy.BuyTea;

         buyDelegate();
     }
}

public class Buy
{
    public void BuyFood()
    {
      Conssole.WriyeLine(" Buy a snail lion powder ");
    }
    public void BuyCake()
     {
      Conssole.WriyeLine(" Buy a cake ");

    }
    public void BuyTea()
    {
       Conssole.WriyeLine(" Buy a cup of milk tea ");
    }

  
}

Anonymous delegate

Anonymous delegation is Use anonymous methods to register on delegates , In fact, the role of delegating and dragging is realized by defining code blocks in delegating

1： Define the entrusted 

 Modifier  delegate  return type   Name of Commission ( parameter list )

2： Instantiation delegation 

 Name of Commission   Delegate object =delegate
{

   Code block ;

};


3: Call anonymous delegate 

 Delegate object ( parameter list );

1： Realize fruit trading 

public class program
{
    public delegate void BuyFruit(double price,double count)

    static void main(string[] arg)
    {

        BuyFurit buyFruit=delegate
        {
           Console.WriteLine(" The total price of fruit is "+price*count);
        };
        buyFruit(3,5);
    }

}

When is delegation applicable

1： Delegate is equivalent to using method as another method parameter , meanwhile , You can also bridge two methods that cannot be called directly , For example, cross thread method calls in multithreading have to use delegates .

2： Delegates enable one method to be passed as a parameter to another , This is the greatest function of entrustment . Using delegates, you can bind methods of the same type to the same variable , When this variable is called, the bound method can be called once , Very convenient .